The Canada-USA border is defined by a series of straight lines connecting border
monuments. In terms of degree confluences, the only part of the border that comes into
play is along the 49th parallel, between the west coast and the great lakes, which the
IBC refers to as
Section M.

This image shows each of the degree confluences from 49°N 123°W to 49°N
96°W, and their relationship with the closest border monument on each side of the
line of longitude for the confluence. Between the pair of monuments on either side of
the confluence longitude the line shows the location of the border. The lines between
the monument pairs are just for illustration - the actual border follows monuments that
are not shown on this image.

The border zig-zags back and forth along the WGS84 49th parallel, but none of the
degree confluences along the 49th parallel are actually on the border, so each
confluence belongs to the country in which it is located.

For Section M
of the boundary, along the 49th parallel, from Monument 0 through Monument 912,
and ignoring differences between NAD83 and WGS84:

The average monument location is 3 seconds north or south of 49 degrees, which
is approximately 90 meters.

The average of all the monument locations, both north and south of 49 degrees,
results in an average location of less than 1 second south of 49 degrees, which
is less than 30 meters.

The monuments that are the farthest north are Monuments 35, 36, and 37, at
49 degrees 0 minutes 8.8 seconds North, and are located on the British Columbia border,
just southeast of the Abbotsford airport.

The monument that is the farthest south is Monument 347, at 48 degrees 59 minutes
48 seconds North, which is located on the Alberta border, to the east of Coutts.